Can you help make this a better article? What good localities have we missed? Can you supply pictures of better specimens than those we show here? Can you give us more and better information about the specimens from these localities? Can you supply better geological or historical information on these localities?

GoethiteFeO(OH) Orthorhombic

Goethite, Pikes Peak, Teller Co., Colorado, USA 4cm

Goethite is found as an supergene oxidizing (weathering) product of many iron minerals. In the near surface, it was an important iron ore mineral developed over banded iron formations. It is found in sedimentary rocks as concretions and was mined from bog ore deposits. It is a component of limonite and is found in the weathered gossans of sulfide rich ore deposits and was used as a prospecting indicator.

Massive specimens of goethite are relatively common with a reniform, botyroidal or stalagtitic habit. These specimens are made of numerous acicular crystals and were found in Cornwall and the states of Michigan, Wisconsin and Minnesota in the USA. Individual crystals are rare, the best ones are found in pegmatites from Colorado. Goethite crystals also are found from many localities as crystals suitable for micromounting. or as inclusions in quartz. While the mineral is a yellow brown in color, iridescent coatings can result in aesthetic specimens. There are numerous good examples of goethite pseudomorphing other iron minerals, especially pyrite, marcasite and siderite.

"Limonite" is nowadays just a general field term for earthy iron oxides, not a species name. So, although theoretically "limonites" could be composed of lepidocrocite, hematite, maghemite, various hydrous iron oxides or oxy-hydroxides, and even powdery jarosite-group species, they are most commonly composed of goethite, so it's fairly safe to label them that way, especially when the streak is yellow-brown, they show no magnetism, and they have been kept dry for a long time (after which the less stable hydrated oxides mostly alter into goethite anyway). I've had a lot of hard brown iron oxides x-rayed. Once in a while they turn out to be mainly hematite, like the christmas-tree shaped pseudos from Egypt, in spite of not having a very red streak, and once one locality turned out to be maghemite (I should have checked it with a magnet before wasting an XRD :( ) and another had a lot of jarosite in it. Never yet found a "limonite" that was lepidocrocite. Even if a sample turned out to be a goethite-bearing mixture, that wouldn't make a "goethite" label wrong.

Dave,I have been working on pseudomorphs and as you can imagine there are a lot of limonite and goethite images that have been uploaded to the image bank and actually I have used a few of the examples that you have shown above in those articles too. I have come to feel that many of the images are probably labeled hematite/goethite/limonite without anyone knowing what they are for sure. Most are probably limonite, that is a mixture of iron oxide minerals which include goethite and limonite. How confident are you that the images in your article here are really mostly pure goethite rather than limonite? Probably the Goethites from the Restormel mine, UK and the Crystal Peak area of Colorado and a couple of others? I often think what the uploaders or the dealers put on their labels and what gets passed on to the captions of our images is rather arbitrary with no grounding in real mineralogy. If you agree you might want to add in the introduction to the article a warning that many of these images may be limonite, a mixture of various iron oxide minerals and not real pure goethite. Perhaps in the captions of those that are know to be pure or nearly pure goethite, it could be emphasized that these are real goethite specimens/crystals. I plan to do this in the pseudomorph articles, at least to the best of my ability.

"Limonite" is nowadays just a general field term for earthy iron oxides, not a species name. So, although theoretically "limonites" could be composed of lepidocrocite, hematite, maghemite, various hydrous iron oxides or oxy-hydroxides, and even powdery jarosite-group species, they are most commonly composed of goethite, so it's fairly safe to label them that way, especially when the streak is yellow-brown, they show no magnetism, and they have been kept dry for a long time (after which the less stable hydrated oxides mostly alter into goethite anyway).

I've had a lot of hard brown iron oxides x-rayed. Once in a while they turn out to be mainly hematite, like the christmas-tree shaped pseudos from Egypt, in spite of not having a very red streak, and once one locality turned out to be maghemite (I should have checked it with a magnet before wasting an XRD :( ) and another had a lot of jarosite in it. Never yet found a "limonite" that was lepidocrocite. Even if a sample turned out to be a goethite-bearing mixture, that wouldn't make a "goethite" label wrong.

A small quarry near Freisen, Saarland, produced fine acicular crystals to over 2 cm (commonly < 1 cm, though). They occur in miarolitic cavities of a melaphyr basalt that are lined with smoky quartz, often together with chabazite. An undisclosed locality in Morocco (usually just described as "High Atlas Mts.") produced similar material, but never with chabazite.

Goethite was mined in NW Connecticut (Ore Hill in particular), western Massachusetts and adjacent New York state for almost 200 years. Many fine specimens are out there, but woefully few are pictured on mindat. I have several and will eventually photograph and post them, but it may be a few weeks...Also micro sprays of acicular golden-brown goethite crystals are known from East Haven, Connecticut. There are some photos up on the Cinque Quarry page: http://www.mindat.org/loc-6789.html and the High Street construction site: http://www.mindat.org/loc-72430.html

Interesting selection of specimens. I love the iron oxide minerals but often find that sellers do not check their material even with simple streaktest to distinguish what is likely hematite from goethite. For that matter the manganese oxides with their gray streak also come into play here. But then as I think Alfredo points out it may take formal testing to be certain regarding some specimens. There are also pieces that vary in streak depending on what part of the rock you check.

Shifting topics here, does anyone know the explanation for the color bands in some massive goethite specimens? It is common in the Great Lakes Iron Ranges of NorthAmerica. In the posted images under "Best Minerals" there are examples from Marquette Co,Michigan and Wisconsin as well as the Minnesota specimen. Sometimes the banding is very regular, almost like tree rings and assume the solution from which crystals form must oscillate in composition. Has anyone seen fine banding in microxls of goethite such as occurs in some linear malachite xls?

George,You question about the cause of color banding in massive goethite specimens would probably draw more attention in one of the other forums rather than here in the Best Minerals section, but you may get lucky and someone will respond to with the information you want. I don't know the answer, but I would expect that the difference would be found in the variable mineralogy of fine grained iron minerals that undoubtedly comprise the bulk of these specimens. Perhaps some grad student has made a study of them.

Please, enter the code that you see below in the input field.
This is for blocking bots that try to post this form automatically. If the code is hard to read, then just try to guess it right.
If you enter the wrong code, a new image is created and you get
another chance to enter it right.